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Seawater samples were collected at the Vertex IV site at 28°N, 155°W in the central North Pacific Ocean. The very old deep waters show low concentrations of dissolved Ce, and the lowest values worldwide of dissolved Ce relative to the other REE, as defined by either the Ce/Nd ratio or the Ce anomaly Ce/Ce ∗ . The very old deep waters in the central North Pacific show the highest concentrations of dissolved strictly trivalent REE, i.e. except for Ce. Within the thermocline region there exist very close linear relations of the REE series with the nutrients PO 4 and NO 3 , but curvature versus nutrient SiO 4 . This and the general about twofold enrichment of deep Pacific versus deep Atlantic of REE and PO 4 , NO 3 , would support the notion that ocean biogeochemical cycling of the REE is coupled with the ocean cycling of organic matter. Multiple regressions of Nd, representing the LREE, and Er, representing the HREE, versus both phosphate and silicate are significant. Nevertheless there is room for the hypothesis of invoking additional net deep water scavenging of mostly the LREE (i.e. Nd) but also the HREE (i.e. Er). There is a trend of increasing REE abundance with increasing atomic number, when the dissolved seawater data at Vertex IV site are normalized versus PAAS reference. This trend is consistent with stabilization in seawater due to stronger inorganic complexation with carbonate ion with increasing atomic number from La to Lu. There are indications for a positive Gd anomaly at Vertex IV site and also in other datasets of dissolved REE in other oceans. Interoceanic comparison between the North Pacific and the Northwest Atlantic shows for the deep Pacific an up to 2.5-fold relative enrichment for the strictly trivalent REE, that is parallel with enrichment of phosphate and nitrate, suggesting REE-cycling along with the ocean cycle of organic matter. The Pacific/Atlantic concentration ratio does not increase with increasing atomic number along the REE series. The deep Pacific shows an up to 3-fold relative Ce depletion versus the deep Atlantic. The deep North Pacific is enriched with Eu relative to the deep Northeast Atlantic, likely due to more emissions of Eu-enriched hydrothermal fluids in the Pacific basin. [ABSTRACT FROM AUTHOR]

We evaluated both the spatial distribution of gadolinium (Gd) and other rare earth elements (REE) in surface waters collected in a transect of San Francisco Bay (SFB) and their temporal variations within the Bay over two decades. The REE were preconcentrated using the NOBIAS PA-1 resin prior to analysis by high-resolution inductively coupled plasma mass spectrometry. Measurements revealed a temporal increase in the Gd anomaly in SFB from the early 1990s to the present. The highest Gd anomalies were observed in the southern reach of SFB, which is surrounded by several hospitals and research centers that use Gd-based contrast agents for magnetic resonance imaging. Recent increases in that usage presumably contributed to the order of magnitude increase in anthropogenic Gd concentrations in SFB, from 8.27 to 112 pmol kg-1 over the past two decades, and reach the northeast Pacific coastal waters. These measurements (i) show that "exotic" trace elements used in new high-tech applications, such as Gd, are emerging contaminants in San Francisco Bay and that anthropogenic Gd concentrations increased substantially over a 20 year period; (ii) substantiate proposals that REE may be used as tracers of wastewater discharges and hydrological processes; and (iii) suggest that new public policies and the development of more effective treatment technologies may be necessary to control sources and minimize future contamination by REE that are critical for the development of new technologies, which now overwhelm natural REE anomalies. [ABSTRACT FROM AUTHOR]

Abstract: The resin NOBIAS-chelate PA-1® was used to develop an off-line pre-concentration and extraction method for rare earth elements (REEs) in seawater prior to quantification using magnetic sector, high resolution, inductively coupled plasma mass spectrometry (HR ICP-MS). The method employed an off-line manifold that is inexpensive, easy to set-up, and allows simultaneous processing of several samples. The method has low blanks and detection limits, which were in the range of 0.01pmolkg−1 to 0.82pmolkg−1, and yields quantitative recovery for all REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) precluding the need to use isotope dilution. The HR ICP-MS allows an integrated, time-averaged signal of the eluent sample, reducing the HR ICP-MS instrument time relative to an in-line extraction procedure. The applicability of the method was demonstrated in a test of the hypothesis that some REEs are being mobilized by anthropogenic activities and are elevated in San Francisco Bay (SFB) and its discharge plume into coastal waters off Central California. This was done by normalizing REE data from the SFB to those of the GEOTRACES Surface Coastal (GSC) reference sample, collected in the Santa Barbara Basin off Southern California. The normalized REE pattern indicated a substantial Gd anomaly of up to 30-fold higher than GSC in the industrial southern reach of the SFB (Lower South Bay), and to a lesser extent in the plume, indicative of anthropogenic Gd inputs, associated with the medical use of Gd-based contrasting agents in magnetic resonance imagery, from the surrounding metropolitan area. Smaller anomalies for Lu and Yb were also observed in the Lower South Bay and plume, which were tentatively attributed to industrial inputs. However, because of the relatively restricted industrial uses of these elements this hypothesis requires further investigation. Ce and Eu anomalies were observed in the northern reaches of the Bay and appeared to be associated with natural redox mediated behavior of these REEs. [Copyright &y& Elsevier]

Highlights: [•] We present Fe and concentrations in the California Current transition zone (TZ). [•] Low levels of coastally upwelled Fe relative to are delivered to the TZ. [•] Cyclonic mesoscale eddies cause a shoaling of the nutricline and ferrocline. [•] Wind curl induced upwelling in the TZ does not deliver enough Fe to the surface. [•] The central California Current TZ exhibits evidence for Fe limiting conditions. [Copyright &y& Elsevier]

Abstract: Coastal upwelling in the central California Current System (cCCS) delivers macro and micronutrients to the surface ocean that fuel biological productivity. Variations in upwelling strength and continental shelf width affect trace metal sources seasonally. The purpose of this study was to investigate various sources and distributions for a suite of dissolved trace metals (Mn, Fe, Co, Ni, Cu, Zn, and Cd) in the cCCS (34–41°N) as well as to determine the effects of biological uptake, physical advection, and mixing processes on trace metal concentrations during the spring and summer upwelling season. Continental shelf sediments did not substantially affect upwelled concentrations of Ni, Zn, and Cd — three typical nutrient-type trace metals. However, shelf sediments provided a significant external source for Mn, Fe, Co, and Cu — scavenged and hybrid-type trace metals. There was no clear seasonal trend in benthic boundary layer (BBL) Fe concentrations; however, higher concentrations of Mn and Co together with lower O2 concentrations were found in the BBL in the late summer compared to early spring. Conversely, there was a higher sedimentary Cu source to the BBL in the early spring before O2 concentrations dropped. Surface transect samples along the Big Sur Coast (May, 2010) and North Coast (August, 2011) demonstrated both mixing and biological assimilation of NO3 − and trace metals. Iron and Zn showed accelerated drawdown relative to NO3 − during both seasons suggesting an increased metal to nitrogen drawdown ratio at higher dissolved metal concentrations. Surface Mn and Co concentrations were higher in the late summer and both showed evidence for accelerated drawdown relative to NO3 −. Cadmium and Ni were strongly correlated with NO3 − indicating that both are affected by a combination of assimilation and regeneration at a constant rate relative to NO3 −; however, Cd showed slightly increased drawdown in aged upwelled waters during the late summer when Zn and Fe concentrations were low. This study provides field trace metal and macronutrient data supporting past laboratory studies suggesting that complex biological interactions are a key control on trace metal distributions and marine biogeochemical cycles. [Copyright &y& Elsevier]

Abstract: A method was developed using the chelating resin Nobias-chelate PA1 in an off-line pre-concentration manifold with magnetic sector inductively coupled plasma mass spectrometry (ICP-MS) detection for analysis of Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb. This multi-element method allows for the simultaneous extraction of eight samples in a closed column manifold. Standard additions to seawater demonstrated quantitative recovery and eliminated the need to use isotope dilution to account for non-quantitative recoveries of the metals on the resin. UV-oxidation of seawater samples before extraction was necessary to provide accurate total dissolved concentrations of Co and Cu. Samples (40mL) were loaded onto the chelating resin column at a pH of 6.2±0.3 after pH adjustment with a basic ammonium acetate (NH4Ac) solution. The columns were rinsed after sample loading with a weak (0.05M) NH4Ac solution to remove the bulk of the major ions in seawater. The trace metals were eluted with 3 to 4mL of 1N Q-HNO3 and analyzed on a magnetic sector ICP-MS. This multi-element method is ideal for high sample throughput and quantification over a broad range of element concentrations with low blanks and detection limits. We report results here from the SAFe and GEOTRACES reference samples as well as the U.S. GEOTRACES Atlantic and Pacific Baseline profiles. [Copyright &y& Elsevier]

Abstract: Trace elements in seawater can be limiting factors of biological productivity, tracers of ocean circulation and biogeochemical processes, and proxies for paleoceanography. The global status of trace elements and their isotopes (TEIs) in the ocean is being explored this decade through an international study of the global marine biogeochemical cycles of TEIs (GEOTRACES). Such an international study has become possible due to recent methodological developments in sampling, preconcentration, and measurement of TEIs. Here, we present an overview of recent methodological developments and initial GEOTRACES intercalibration activities for obtaining data about TEIs that are accurate, precise, and intercomparable. [Copyright &y& Elsevier]

Abstract: The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000nM and 18,000nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf. [Copyright &y& Elsevier]

There has been a growing interest in the cause and impact of hypoxic regions known as "dead zones" that have increasingly appeared along the west coast of the United States and have caused widespread destruction to the crab and fishing industry in this upwelling region. Here, we present results that demonstrate that the hypoxic conditions in the water column over the continental shelf result in a marked increase in iron(ll) concentrations, which contribute to elevated dissolved and labile particulate iron concentrations. These elevated dissolved iron(ll) concentrations resuft from two factors: (1) the hypoxic water column allows extremely elevated iron(lI) concentrations in reducing porewaters to exist close to the sediment water interlace, leading to an increased flux of iron(lI) from the sediments; (2) the low oxygen, low pH, and low temperatures within the bottom boundary layer act in concert to markedly slow down the oxidation rate of Fe(ll). During upwelling conditions, this process can result in a greatly enhanced source of Fe available to upwell to surlace waters, potentially increasing phytoplankton productivity, which can, in turn, lead to enhanced export flux, driving the system further into hypoxic or suboxic conditions. [ABSTRACT FROM AUTHOR]

Abstract: The distributions of particulate elements (Al, P, Mn, Fe, Co, Cu, Zn, Cd, and Pb), dissolved trace metals (Mn, Fe, Co, Cu, Zn, and Cd), and dissolved nutrients (nitrate, phosphate, and silicic acid) were investigated in the Gulf of the Farallones, a region of high productivity that is driven by the dynamic mixing of the San Francisco Bay plume, upwelled waters, and California coastal surface waters. Particulate metals were separated into >10 and 0.4–10μm size-fractions and further fractionated into leachable (operationally defined with a 25% acetic acid leach) and refractory particulate concentrations. Dissolved metals (< 0.4μm pore-size filtrate) were separated into colloidal (0.03–0.4μm) and soluble (<0.03μm) fractions. The percent leachable particulate fractions ranged from 2% to 99% of the total particulate concentration for these metals with Mn and Cd being predominantly leachable and Fe and Al being predominantly refractory. The leachable particulate Pb concentration was associated primarily with suspended sediments from San Francisco Bay and was a tracer of the plume in coastal waters. The particulate trace metal data suggest that the leachable fraction was an available source of trace metal micronutrients to the primary productivity in coastal waters. The dissolved trace metals in the San Francisco Bay plume and freshly upwelled surface waters were similar in concentration, with the exception of Cu and Co, which exhibited relatively high concentrations in plume waters and served as tracers of this water mass. The dissolved data and estimates of the plume dynamics suggest that the impact of anthropogenic inputs of nutrients and trace metals in the San Francisco Bay plume contributes substantially to the concentrations found in the Gulf of the Farallones (10–50% of estimated upwelled flux values), but does not greatly disrupt the natural stoichiometric balance of trace metal and nutrient elements within coastal waters given the similarity in concentrations to sources in upwelled water. In all, the data from this study demonstrate that the flux of dissolved nutrients and bioactive trace metals from the San Francisco Bay plume contribute to the high and relatively constant phytoplankton biomass observed in the Gulf of the Farallones. [Copyright &y& Elsevier]

Abstract: A method employing dual competitive ligand exchange followed by solid phase extraction (CLE-SPE) for characterizing the complexation of inorganic Hg(II) in natural waters is described. This method employs parallel use of two competing ligands: diethyldithiolcarbamate (DEDC), which forms hydrophobic complexes with Hg(II), and thiosalicylic acid (TSA), which forms hydrophilic complexes with Hg(II). Inorganic mercury complexed by natural and competing ligands are separated based on hydrophobicity using C18 solid phase extraction columns. Data modeling allows for the calculation of the concentration and conditional stability constants of natural ligands capable of complexing Hg(II) in both the operationally defined hydrophilic and hydrophobic fractions. The use of multiple ligand concentrations, and thus multiple analytical windows, to characterize different ligand classes within both of these two fractions is described. Studies of the kinetics of the ligand exchange involved, potential for changes in the stability of natural ligands during freezing and thawing, potential breakthrough during solid phase extraction, as well as the method''s precision and estimation of error, are presented and discussed. Results from the application of the method to natural freshwaters demonstrated that in the limited samples collected over 99.99% of the ambient inorganic mercury is strongly complexed by ligands with conditional stability constants (, Hg2+) on the order of 1030, values similar to that of reduced sulfur ligands. At ambient conditions 85–90% of the mercury exists in hydrophobic complexes in these freshwaters, but strong Hg-binding ligands exist in both the hydrophobic and hydrophilic fractions. [Copyright &y& Elsevier]

Abstract: A vertical mixing event was simulated in shipboard incubation experiments on the mid-continental shelf of the eastern Bering Sea to investigate Fe and Zn cycling between the soluble (<0.03 μm or 200 kDa), colloidal (0.03–0.2 μm), and particulate (0.2–10 μm, >10 μm) size-fractions. The particulate Fe and Zn were further separated into chemically labile (25% acetic acid-leachable) and refractory pools. The experiment employed 57Fe (+0.90 nM) and 68Zn (+0.99 nM) as stable, low-abundance isotope amendments to the soluble fraction, and the exchange of Fe and Zn between the different physico-chemical fractions was measured using high resolution-inductively coupled plasma-mass spectrometry (HR-ICP-MS). More than 50% of the added 57Fe partitioned to the colloidal fraction within 45 min of adding the tracer. Both the 57Fe and 56Fe colloidal fraction were removed from the dissolved phase at a faster rate than the soluble Fe fraction. In contrast, the colloidal 66Zn and 68Zn concentrations remained constant over the 5-day experiment, suggesting a unique removal mechanism for colloidal Fe. The net removal of dissolved 57Fe was observed to be 3 to 4 times more rapid than dissolved 56Fe, which can be attributed to the regeneration of particulate Fe. Using a simple first-order model, it was determined that the net removal of 2.0 nM of dissolved Fe during the experiment was a consequence of dynamic cycling, whereby 2.9 nM of particulate Fe was regenerated and contributed to an overall removal of 4.9 nM of Fe from the dissolved phase. The amended 68Zn tracer resided in the soluble fraction and was assimilated by the diatom biomass (>10 μm size-fraction) at the same rate as 66Zn. This similarity in rates suggests that nearly all of the net removal of Zn was due to assimilation and that regeneration did not play a significant role in Zn cycling within the incubation experiment. This research demonstrates the advantage of using low-abundance isotopes as tracers and the importance of particulate and colloidal Fe in the overall biogeochemical cycling of Fe in ocean surface waters. [Copyright &y& Elsevier]

Abstract: The spatial distributions of dissolved manganese and nutrients were examined in the Columbia River plume off Oregon and Washington during the summer of 2004 and 2005 as part of the River Influence on Shelf Ecosystems (RISE) program. Factors influencing the hydrochemical characteristics of the freshly formed and aged Columbia River plume were investigated. Hydrographic data and nutrient concentrations were used to delineate three distinct water sources for the Columbia River Plume: California Current surface water, coastal upwelled water, and Columbia River water. The warm, intermediate salinity, nutrient poor California Current water contains low levels of dissolved manganese (<5 nM) and silicic acid (<5 μM), and is depleted in nitrate. The cold, high salinity, nutrient rich, freshly upwelled water is highly variable (2–20 nM) in dissolved manganese and can be as high as ∼45 μM in silicic acid and ∼30 μM nitrate. The variable Columbia River has summer temperatures ranging from ∼13 to 24 °C, high silicic acid concentrations (ranging from ∼120 to 200 μM), and lower nitrate concentrations (ranging from ∼2 to 20 μM). During the summer, the concentrations of silicic acid and dissolved manganese can exceed 100 μM and 200 nM, respectively, in near-field Columbia River plumes. These values are markedly greater than those of surface coastal waters (even during upwelling conditions). As the plume advects and mixes, the concentrations of these two constituents remain relatively high within plume waters. The concentrations of dissolved manganese in the near-field plume vary with tidal amplitude, exhibiting much higher concentrations for a given salinity during spring tides than during neap tides. For example, the Columbia River plume at a salinity of 20 has a concentration of dissolved manganese of ∼240 nM during spring tides, as compared to only ∼60 nM during low amplitude tides. Silicic acid concentrations in the near-field plume remain relatively constant throughout the tidal month. Calculations indicate there is roughly an equivalent yearly delivery of dissolved manganese and silicic acid to the coastal waters off Oregon and Washington by upwelled waters and by the Columbia River plume. [Copyright &y& Elsevier]

Abstract: The influence of the Columbia River plume on the distributions of nitrate and iron and their sources to coastal and shelf waters were examined. In contrast to other large estuaries, the Columbia River is a unique study area as it supplies very little nitrate (5 μM) and iron (14–30 nM) at salinities of 1–2 to coastal waters. Elevated nitrate and dissolved iron concentrations (as high as 20 μM and 20 nM) were observed, however, in the near field Columbia River plume at salinities of 20. Surface nitrate concentrations were higher than observed in the Columbia River itself and therefore must be added by entrainment of higher nitrate concentrations from subsurface coastal waters. Tidal flow was identified as an important factor in determining the chemical constituents of the Columbia River plume. During the rising flood tide, nitrate and iron were entrained into the plume waters resulting in concentrations of 15 μM and 6 nM, respectively. Conversely, during the ebb tide the concentrations of nitrate and total dissolved iron were reduced to 0.3–3 μM and 1–2 nM, respectively, with a concomitant increase in chlorophyll a concentrations. As these plume waters moved offshore the plume drifted directly westward, over a nitrate depleted water mass (<0.2 μM). The plume water was also identified to move southwards and offshore during upwelling conditions and nitrate concentrations in this far field plume were also depleted. Iron concentrations in the near-field Columbia River plume are sufficient to meet the biological demand. However, due to the low nitrate in the Columbia River itself, nitrate in the plume is primarily dependent on mixing with nitrate rich, cold, high salinity subsurface waters. Without such an additional source the plume rapidly becomes nitrate limited. [Copyright &y& Elsevier]

Abstract: Dissolved copper speciation and total dissolved copper concentrations were determined at six San Francisco Bay sites in January and March of 2003. Multiple analytical windows were incorporated into an established competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) method, which employs salicylaldoxime (SA) as the added competitive ligand for speciation analyses. The titration results were integrated into [CuT *] versus log [Cu2+] plots, combining data from each of the different competing ligand concentrations and providing a powerful approach to visually interpret the variation in [Cu2+] as the natural Cu-binding ligands in the sample are titrated over a wide range of [CuT]. In addition, the data for different analytical windows were interpreted with Langmuir and Scatchard linearization techniques to estimate natural Cu-binding ligand concentrations [L i ] and conditional stability constants K CuLi,Cu2+ cond. All results indicate that ambient ligand concentrations exceed total dissolved copper concentrations at each site, with dissolved copper greater than 99.9% complexed by the strong copper-binding L 1 ligand class. The [Cu2+] does not exceed 10−13 M at any site, a concentration sufficiently below the toxicity threshold for microorganisms. Thus, the excess of strong Cu-binding ligands appears to effectively buffer free Cu2+ at low concentrations and the existing levels of copper do not impair San Francisco Bay. [Copyright &y& Elsevier]

Abstract: Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L1-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu2+] in the San Francisco Bay estuary. [Copyright &y& Elsevier]

Abstract: Surface water transects and vertical profiles for dissolved iron, macronutrients, chlorophyll a (Chl a), and hydrographic data were obtained in the Peru upwelling regime during August and September 2000. The supply of the micronutrient iron, relative to that of the macronutrients nitrate, phosphate and silicic acid, is shown to play a critical role in allowing extensive diatom blooms to develop in the Peru upwelling system. The extremely high-chlorophyll “brown waters of Peru” (with Chl a concentrations between 20 and 45 μg/l) result from massive diatom blooms with maximal photochemical efficiencies (Fv/Fm >0.6) occurring in the iron-rich upwelling region observed over the broad continental shelf off northern and central Peru. The source of the upwelled water in this region is the nutrient-rich subsurface countercurrent in contact with the organic-rich shelf sediments. This subsurface shelf water is suboxic and has extremely high concentrations of dissolved Fe (>50 nM) in the near-bottom waters. In marked contrast, relatively low-chlorophyll “blue waters” (Chl a <2 μg/l) with low concentrations of dissolved Fe (<0.1 nM) and high unutilized macronutrient concentrations are observed in the coastal upwelled waters along the southern coast of Peru and in the offshore regions of the Peru Current. Southern Peru is a region without a wide shelf to serve as a source of iron and, as a result, dissolved Fe concentrations in the near-bottom suboxic waters of this region are an order-of-magnitude lower than observed off northern and central Peru. In addition, the offshore Peru Current is a broad, Fe-limited, high-nitrate, lower than expected chlorophyll region extending hundreds of kilometers offshore into the northeast region of the South Pacific subtropical gyre and northwestward into the South Equatorial Pacific. [Copyright &y& Elsevier]

Additions of the low occurrence stable isotopes 61Ni, 65Cu, and 68Zn were used as tracers to determine the exchange kinetics of metals between dissolved and particulate forms in laboratory studies of natural water and suspended sediments from South San Francisco Bay, CA. Dissolved metal isotope additions were made so that the isotope ratios (rather than total metal partitioning) were significantly altered from initial ambient conditions. Dissolved metal concentrations were determined using an organic ligand sequential extraction technique followed by analysis with high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS). Exchangeable particulate concentrations were extracted using a 20% acetic acid leach followed by determination using HR-ICPMS. Equilibrium and kinetic sorption parameters were quantified according to a general model for trace metal partitioning assuming pseudo-first-order kinetics. Partition coefficients (KD) were tracked as a function of time over the fortnight experiment. For Ni, Cu, and Zn the initial ambient KD values were found to be 103.65, 103.88, and 104.52 L kg−1, respectively. As a result of the dissolved metal isotope additions, the partition coefficients for all three metals dropped and then increased back to near ambient KD values after 14 days. Curve-fitting concentration versus time profiles from both dissolved and exchangeable particulate data sets allowed determination of kinetic rate constants. The best estimates of forward and backward kinetic rate constants for Ni, Cu, and Zn respectively are k′f = 0.03, 0.07, 0.12 d−1 and kb = 0.13, 0.12, 0.15 d−1. These results predict that sorption equilibria in South Bay should be reached on the order of a month for Ni, on the order of 3 weeks for Cu, and on the order of 2 weeks for Zn. Together, the dissolved and exchangeable particulate data indicate more sluggish sorption kinetics for Ni than for Cu and Zn and suggest that different chemical forms control the speciation of these three metals in South Bay. Order of magnitude metal sorption exchange rates were estimated using these kinetic results. These calculations indicate that sorption exchange between dissolved and suspended particulate phases can cause dynamic internal cycling of these metals in South San Francisco Bay. [Copyright &y& Elsevier]

A flow injection analysis (FIA) catalytic spectrophotometric method for the determination of dissolved iron in seawater was further developed to yield a more sensitive assay with a low detection limit. The method employs an initial sample acidification step followed by an iron pre-concentration step involving an in-line 8-hydroxy-quinoline (8-HQ) metal-chelating resin column. The copper capacity and elution efficiency, as well as the iron FIA performance of three trace-metal clean resins were compared, resulting in the selection of a clean silica gel support for the 8-HQ ligand. The concentrated sample is eluted from the resin with an acidic carrier and mixed with reagents, initiating an iron-catalyzed, color-forming reaction. Increasing the reaction temperature from 18 to 30 °C doubled the sensitivity; reaction temperature control was necessary to obtain good reproducibility in the field. Reagent blanks were as low as 0.05 nM and a detection limit of 0.016 nM was obtained from three times the S.D. of a 0.06 nM seawater sample repeated six times. A 0.06 nM detection limit was calculated from shipboard experiments where total dissolved iron was determined for 10 different samples from the same station. The instrumental sensitivity and precision evolved to the point where the blank associated with the technique is the major factor influencing its detection limit. [Copyright &y& Elsevier]

Examines the potential for silver to be strongly bound by organic ligands in marine waters using a new competitive equilibration/solvent extraction technique. Establishing a competition for silver between ligands already present in the sample; Indication that the chemical speciation of silver in seawater is dominated by inorganic chloride complexes.

Presents a study on the uptake of lipophilic organic compounds, indicating that they enter the cell by diffusion across the plasma membrane. Elucidation of the mechanism in metal assimilation; Backgrounder on the uptake of these compounds; Materials and methods used; Diffusion of lipophilic organic metal compounds.

Presents research which demonstrated that phytoplankton are iron-limited in parts of the California coastal upwelling region. Phytoplankton growth limited by iron availability; Addition of iron to high-nitrate, low-chlorophyll (HNLC) regimes; Silicic acid:nitrate (Si:N) uptake ratios; Diatoms stressed by lack of iron; Si:cell, Si:C and Si:pigment ratios in diatoms; Implications of research.

Cadmium (Cd) is not generally considered a nutrient element, but behaves like a nutrient in the oceans and might play an important role in ocean biology after all. The relationship between Cd and the nutrient phosphate (PO 4 ) has been studied for over 40 yrs, but the debate on the driving mechanism and reason behind the ‘kink’, a change in the steepness of the slope is ongoing. Using new data of high accuracy and spatial resolution covering the West-Atlantic Ocean from north to south, in combination with a robust extended optimum multiparameter (eOMP) water mass model, we show that mixing between different water masses is the dominant factor explaining the observed correlation and its kink. Regeneration of Cd via remineralisation explains the smaller scale variability, notably in the surface ocean. Observations imply the availability of Cd in surface waters determines the Cd-uptake and thus the Cd:PO 4 remineralisation ratio. This ratio is variable between different ocean regions, notably between the northern and southern high latitude oceans. Due to their role in deep water formation, both the northern and southern high latitude oceans are a driving factor in the Atlantic and global Cd and PO 4 relation. Outside the Atlantic Ocean, the classical kink is not expected, but the relationship is by no means linear. Most likely, this is due to the interaction between low latitude surface waters and subsurface waters from high latitude origin, but more data are required to assess this in detail. [ABSTRACT FROM AUTHOR]

The physicochemical speciation of dissolved iron (Fe) across natural dissolved Fe gradients in the oceanic and shelf domains of the southeastern Bering Sea was examined in surface and subsurface samples using competitive ligand exchange-adsorptive cathodic stripping voltammetry with the added ligand salicylaldoxime. Two ligand classes were measured in all samples, a stronger L1 ligand class and a weaker L2 ligand class. Conditional stability constants for both ligand classes were comparable between surface and subsurface samples, with mean log Kcond FeL1,Fe0 = 11.5 ± 0.3 and mean log KcondFeL2,Fe0 = 10.3 ± 0.3 in surface samples, and mean log KcondFeL1,Fe0 = 11.4 ± 0.2 with a weaker ligand and mean log KcondFeL2,Fe0 of 10.2 ± 0.2 in subsurface samples. The concentrations of dissolved Fe were strongly correlated with ambient stronger L1 ligand concentrations for all samples with dissolved Fe concentrations greater than 0.2 nmol L-1. In samples with dissolved Fe concentrations less than 0.2 nmol L-1, large and variable excesses of L1 ligand concentrations were measured, coincident with observed Fe stress or limitation on the ambient phytoplankton. These observations suggest that the phytoplankton community is readily able to access dissolved Fe from the FeL1 complex, resulting in excess L1 in these waters. The available speciation data from other sources indicate that a significant correlation exists between dissolved Fe and L1 ligand concentrations in samples with intermediate dissolved Fe, and this is a seemingly ubiquitous feature of dissolved Fe cycling in the marine environment. [ABSTRACT FROM AUTHOR]

Abstract: The coastal northern Gulf of Alaska receives significant fluvial inputs from the numerous glaciers and rivers that border the region. The distribution of dissolved (soluble and total) and particulate aluminum (leachable and total) was examined in coastal surface water transects and vertical profile samples from shelf stations in the northern Gulf of Alaska in August and September 2007. Both dissolved and particulate aluminum concentrations were dramatically increased in low-salinity plumes, indicative of the significant riverine/glacial input to coastal waters in the region. The percent-leachable particulate Al fraction in these low-salinity plumes was quite low (∼7%), indicative of the large refractory nature of the lithogenic material being delivered to the coastal waters. A consistency in Si:Al ratios from different time periods in the freshwater endmembers that mix to form the low-salinity plumes is discussed in terms of the weathering of biotite in this region. The dissolved Al in these coastal waters appears entirely in the soluble (<0.03µm) fraction, likely a consequence of the freshwater sources to the region being very low in dissolved organic carbon and organic colloidal complexes. An extreme decreasing gradient of dissolved Al in surface waters was observed moving offshelf and into the waters of the Alaskan subarctic gyre where some of the lowest dissolved Al concentrations reported in the world ocean were observed. A high-degree of particle scavenging of dissolved Al in the coastal waters is discussed with a residence time of dissolved Al in coastal shelf waters estimated to be ∼10days. [ABSTRACT FROM AUTHOR]

Abstract: Coastal waters in the northern Gulf of Alaska (GoA) are considered iron-rich and nitrate-poor, in contrast to the iron-poor, high-nitrate, low chlorophyll (HNLC) waters of the central GoA. The degree of mixing between these two regimes, enhanced by mesoscale eddies, is essential to the high productivity observed in the region. As part of a study on iron delivery to the central GoA via mesoscale eddies, extensive work was focused on characterizing the coastal endmember, the Alaska Coastal Current. In surface Alaskan coastal waters between Yakutat and the Kenai Peninsula, dissolved iron concentrations ranged from 0.5 to 4.1nM with an average of ∼2nM. In contrast, leachable particulate iron concentrations were much higher and more variable, ranging from over 1μM in the Alsek River plume to less than 5nM at the base of Cook Inlet. Cross-shelf transport of both surface and subsurface dissolved iron and leachable particulate iron was observed. Throughout the study area, leachable particulate iron values were at least an order of magnitude higher than dissolved values, suggesting that the system''s ability to solubilize this large concentration of leachable particulate iron is overwhelmed by the massive input of glacial-derived particulate iron. Nevertheless, suspended leachable particulate iron remains available for exchange to the dissolved phase and is suggested to maintain a relatively constant (∼2nM) source of dissolved iron in the coastal GoA. [Copyright &y& Elsevier]

Abstract: Surface transects and vertical profiles of total and leachable particulate Fe, Mn, Al and P, along with dissolved and soluble Fe were obtained during August 2003 in the southeastern Bering Sea. High concentrations of leachable particulate Fe were observed in the bottom waters over the Bering Sea shelf with an unusually high percentage of the suspended particulate Fe being leachable. Leachable particulate Fe averaged 81% of total particulate Fe, and existed at elevated concentrations that averaged 23 times greater than dissolved Fe in the isolated cool pool waters over the mid shelf where substantial influence of sedimentary denitrification was apparent. The elevated leachable particulate Fe is suggested to be a result of sedimentary Fe reduction in surficial sediments, diffusion of Fe(II) from the sediments to the bottom waters, and subsequent oxidation and precipitation of reduced Fe in the overlying bottom waters. Eddies and meanders of the Bering Slope Current can mix this Fe-rich water into the Green Belt at the outer shelf-break front. Elevated levels of leachable particulate Fe were observed in surface waters near the Pribilof Islands where enhanced vertical mixing exists. Storm events and/or cooling during fall/winter with the resultant destruction of the thermally stratified two-layer system can also mix the subsurface water into surface waters where the elevated leachable particulate Fe is a substantial source of biologically available Fe. [Copyright &y& Elsevier]

Abstract: The NSF-sponsored Coastal Ocean Processes Wind Events and Shelf Transport (WEST) experiment investigates the interplay between wind-driven transport and shelf productivity; while eastern boundary shelves are characterized by high productivity due to upward fluxes of nutrients into the euphotic zone, wind forcing also represents negative physical and biological controls via offshore transport and deep (light-limiting) mixing of primary producers. Although this interaction has been well documented for eastern boundary systems generally and for California specifically, one of the primary goals of WEST was to characterize more fully the interplay between positive and negative effects of wind stress, which result in the consistently elevated biological productivity in these shelf regions. During 3 month-long summer cruises (2000–2002) we observed extremes in upwelling/relaxation, using both in situ instrumentation and remotely sensed data. Relationships between optical and physical properties were examined, with emphasis on biogeochemical implications. During 2000, the WEST region was optically dominated by phytoplankton and covarying constituents. During 2001 and 2002, periods of more intense upwelling favorable winds, we observed a transition to optical properties dominated by detrital and inorganic materials. In all years, the continental shelf break provided a natural boundary between optically distinct shelf and open ocean waters. During 2002, we obtained discrete trace-metal measurements of particulate iron and aluminum; we develop a bio-optical proxy for acetic-acid leachable iron from backscatter and fluorescence, and demonstrate that particulate iron is not well correlated to traditional upwelling proxies such as macronutrients, temperature, and salinity. We conclude that the shelf break between ca. 100 and 200m water depth serves as a natural break point between coastal and oceanic water masses in this region, and that the elevated biomass and productivity associated with this eastern boundary current regime is dominated by these iron rich, shallow shelf waters. [Copyright &y& Elsevier]

The supported liquid membrane (SLM) is a promising separation and preconcentration technique that is well- suited for trace metal speciation in natural waters. The technique is based on the selective complexation of metal ions by a hydrophobic ligand (carrier) dissolved in a water- immiscible organic solvent immobilized in a porous, inert membrane. This membrane separates two aqueous solutions: the test (or donor) solution and the strip (or acceptor) solution. The metal carrier complex is transported by diffusion across the membrane from the source to the strip solution where metal ions are back-extracted. The technique offers great potential to tune the selectivity by incorporating different complexing ligands in the membrane. A SLM was used to analyze the dissolved (<045 μm) copper speciation from two sites in the San Francisco Bay estuary; Dumbarton Bridge, [Cu]total &ap; 27 nM, and San Bruno Shoals, [Cu]total &ap; 23 nM. The sites were also characterized independently by differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE). The SLM employed 10 mM lasalocid, a naturally occurring carboxylic polyether lonophore, in nitrophenyl octyl ether (NPOE) as the membrane complexing ligand, supported by a microporous, poly- propylene, hydrophobic membrane. This is the first study where SLM technique has been compared with an independent speciation technique in marine waters. Results of copper speciation measurements from Dumbarton Bridge, a site in South San Francisco Bay where copper speciation has been well-characterized in previous studies using various voltammetric techniques, indicated that only about 3% (0.9 nM) of the total dissolved copper was SLM labile. The corresponding DPASV labile copper fraction was <0.4% (<0.1 nM) of total dissolved copper. The concentration of total copper binding ligands measured by the membrane technique was 471 nM as compared to 354 nM measured by DPASV, more than 1 order of magnitude higher than the total dissolved copper concentration. The SLM measurements were consistent with earlier copper speciation measurements that were made in South San Francisco Bay using other voltammetric stripping techniques. [ABSTRACT FROM AUTHOR]

We compare the relative contribution of large phytoplankton (>5 and >10 µm) to uptake rates of carbon (C), nitrate (NO3-), and dissolved silicon (Si) and uptake ratios of Si:NO3- and Si:C in Monterey Bay, California (a high-iron region) with three low-iron regions in the eastern tropical Pacific: the Costa Rica upwelling dome, Humboldt current, and Peru upwelling. We also demonstrate the effect of iron enrichment on the above parameters in the latter three regions. In Monterey Bay waters, the µ5-µm size fraction accounted on average for the majority of particulate organic C and was responsible for 92% of total C uptake, 81% of total NO3- uptake, and 98% of total Si uptake, In contrast, in low-iron eastern tropical Pacific waters, the >5-µm size fraction accounted for less than half of the particulate organic C and was responsible for a substantially smaller proportion of total C and NO3- uptake: 27-43% for C and 34-59% for NO3-. Iron enrichment experiments in the eastern tropical Pacific resulted in much higher NO3-, C, and Si uptake rates, although increases were restricted to cells in the >5-µm size fraction. Si:NO3- and Si:C uptake ratios decreased after iron addition at most locations, and decreases were a direct result of lower Si : NO3- and Si : C uptake ratios in the >5-µm size fraction. Our results suggest that iron availability is a major factor regulating primary production, new production, Si uptake, and Si:NO3- and Si:C uptake ratios in the larger phytoplankton size classes in high-nitrate, low-chlorophyll (HNLC) regions in the eastern tropical Pacific. [ABSTRACT FROM AUTHOR]

Complexometric titrations are the primary source of metal speciation data for aquatic systems, yet their interpretation in waters containing humic and fulvic acids remains problematic. In particular, the accuracy of inferred ambient free metal ion concentrations and parameters quantifying metal complexation by natural ligands has been challenged because of the difficulties inherent in calibrating common analytical methods and in modeling the diverse array of ligands present. This work tests and applies a new method of modeling titration data that combines calibration of analytical sensitivity (S) and estimation of concentrations and stability constants for discrete natural ligand classes ([L[sub i]][sub T] and K[sub i]) into a single step using nonlinear regression and a new analytical solution to the one-metal/twoligand equilibrium problem. When applied to jointly model data from multiple titrations conducted at different analytical windows, it yields accurate estimates of S, [L[sub i]][sub T], K[sub i], and [Cu[sup 2+]] plus Monte Carlo-based estimates of the uncertainty in [Cu[sup 2+]]. Jointly modeling titration data at lowand high-analytical windows leads to an efficient adaptation of the recently proposed "overload" approach to calibrating ACSV/CLE measurements. Application of the method to published data sets yields model results with greater accuracy and precision than originally obtained. The discrete ligand-class model is also re-parametrized, using humic and fulvic acids, L[sub 1] class (K[sub 1] = 10[sup 13] M[sup -1]), and strong ligands (L[sub S]) with K[sub S] » K[sub 1] as "natural components". This approach suggests that Cu complexation in NW Mediterranean Sea water can be well represented as 0.8 ± 0.3/0.2 mg humic equiv/L, 13 ± 1 nM L[sub 1], and 2.5 ± 0.1 nM L[sub S] with [CU][sub T] = 3 nM. In coastal seawater from Narragansett Bay, RI, Cu speciation can be modeled as 0.6 ± 0.1 mg humic equiv/L and 22... [ABSTRACT FROM AUTHOR]

The measured concentrations of cadmium, cobalt, copper, nickel, lead, zinc, and manganese in acidified (pH<2) estuarine water samples analyzed for total dissolved trace metal concentrations using on-line chelating resin column partitioning with inductively coupled plasma-mass spectrometry (CRCP-ICP-MS) were compared to those analyzed by graphite furnace atomic absorption spectrometry (GFAAS) after liquid–liquid extraction using a combination of 1-pyrrolidinedithiocarbamate/diethyldithiocarbamate (PDC/DDC). Although there was good agreement between the two sets of analyses for cadmium, lead, manganese, and zinc concentrations, those of cobalt, copper, and nickel determined by CRCP-ICP-MS were found to be 10–20% lower than those determined by solvent-extraction GFAAS. The different yields were positively correlated (R>0.961, simple linear regression) to the dissolved organic carbon (DOC) concentration of the samples. Good agreement between the two methods for cobalt and copper was achieved after ultraviolet (UV) digestion of the acidified samples. Samples collected from the South Bay of the San Francisco Estuary with high DOC showed the greatest difference for cobalt, copper, and nickel which is tentatively attributed to complexation with humic material for copper and cobalt and strong synthetic chelating agents such as ethylenediaminetetraacetic acid (EDTA) for nickel. This is consistent with previous studies on copper, nickel and cobalt complexation in this region. We recommend UV digestion of acidified estuarine samples prior to multi-element analysis by chelating resin flow injection ICP-MS methods. [Copyright &y& Elsevier]

A flow injection inductively coupled plasma magnetic sector mass spectrometry (FI-ICP-MS) method was developed for the analysis of Cd, Cu, Ni, Zn, and Mn in estuarine waters. The method uses just greater than 3 ml sample, and employs an automated on-line preconcentration step using a metal chelating resin (Toyopearl AF-Chelate 650 M). Acidified samples for the analysis of Cd, Cu, Ni, and Zn were buffered on-line to pH of 5.6±0.2 with ammonia acetate just prior to loading onto the chelating resin, while samples for Mn analysis were adjusted to pH of 9.0±0.2 prior to concentration. Limits of detection were: Cd=1.4 ng l−1 (0.013 nM), Cu=17 ng l−1 (0.27 nM), Ni=28 ng l−1 (0.48 nM), Zn=46 ng l−1 (0.70 nM), and Mn=86 ng l−1 (1.6 nM). The blank concentrations were less than 1.5% of the SLEW-2 concentrations for each element analyzed, except Ni, which had a significant, but very constant blank from the Ni cones used. The detection limits were less than 5% of the concentrations observed in the San Francisco Bay estuarine samples, with the exception of Zn where the detection limit was 10% of the concentration of lowest San Francisco Bay sample analyzed. Using the FI preconcentration technique, we conducted medium resolution scans of potential isobaric interferences (mass units 55–66) using a magnetic sector ICP-MS to identify a number of interferent complications with evaluating certain isotopes, especially, 59Co, and 60Ni. Investigations of potential interferents illustrate the importance of appropriate isotope selection and, in some instances, the need to perform blank corrections with both an instrumental and a matrix blank. The method was verified by the analysis of an estuarine water standard reference materials (SLEW-2), and San Francisco Bay samples with previously reported values. Six estuarine samples run in triplicate generated the following average precision (presented as % R.S.D.); Cd=4.2%, Cu=3.2%, Ni=3.3%, Zn=4.4%, and Mn=2.2%. [Copyright &y& Elsevier]

Coastal upwelling of nutrients and metals along eastern boundary currents fuels some of the most biologically productive marine ecosystems. Although iron is a main driver of productivity in many of these regions, iron cycling and acquisition by microbes remain poorly constrained, in part due to the unknown composition of organic ligands that keep bioavailable iron in solution. In this study, we investigated organic ligand composition in discrete water samples collected across the highly productive California Coastal upwelling system. Siderophores were observed in distinct nutrient regimes at concentrations ranging from 1 pM to 18 pM. Near the shallow continental shelf, ferrioxamine B was observed in recently upwelled, high chlorophyll surface waters while synechobactins were identified within nepheloid layers at 60–90 m depth. In offshore waters characterized by intermediate chlorophyll, iron, and nitrate concentrations, we found amphibactins and an unknown siderophore with a molecular formula of C33H58O8N5Fe. Highest concentrations were measured in the photic zone, however, amphibactins were also found in waters as deep as 1500 m. The distribution of siderophores provides evidence for microbial iron deficiency across a range of nutrient regimes and indicates siderophore production and acquisition is an important strategy for biological iron uptake in iron limited coastal systems. Polydisperse humic ligands were also detected throughout the water column and were particularly abundant near the benthic boundary. Our results highlight the fine‐scale spatial heterogeneity of metal ligand composition in an upwelling environment and elucidate distinct sources that include biological production and the degradation of organic matter in suboxic waters. [ABSTRACT FROM AUTHOR]

Diatoms are prominent eukaryotic phytoplankton despite being limited by the micronutrient iron in vast expanses of the ocean. As iron inputs are often sporadic, diatoms have evolved mechanisms such as the ability to store iron that enable them to bloom when iron is resupplied and then persist when low iron levels are reinstated. Two iron storage mechanisms have been previously described: the protein ferritin and vacuolar storage. To investigate the ecological role of these mechanisms among diatoms, iron addition and removal incubations were conducted using natural phytoplankton communities from varying iron environments. We show that among the predominant diatoms, Pseudo-nitzschia were favored by iron removal and displayed unique ferritin expression consistent with a long-term storage function. Meanwhile, Chaetoceros and Thalassiosira gene expression aligned with vacuolar storage mechanisms. Pseudo-nitzschia also showed exceptionally high iron storage under steady-state high and low iron conditions, as well as following iron resupply to iron-limited cells. We propose that bloom-forming diatoms use different iron storage mechanisms and that ferritin utilization may provide an advantage in areas of prolonged iron limitation with pulsed iron inputs. As iron distributions and availability change, this speculated ferritin-linked advantage may result in shifts in diatom community composition that can alter marine ecosystems and biogeochemical cycles. [ABSTRACT FROM AUTHOR]

Summary: Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient‐rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift‐up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo‐nitzschia. Here, we show that certain bloom‐forming diatoms exhibit a distinct transcriptional response that coordinates shift‐up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co‐expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment. [ABSTRACT FROM AUTHOR]

Precise and accurate quantification of Ag and platinum group elements in marine, estuarine and riverine waters is challenging due to the complex matrices and ultra-low concentrations in the pmol kg − 1 and fmol kg − 1 range. A methodological approach has been developed for the analysis of Ag and Pt in seawater based on the extraction of their anionic chloro-complexes utilizing the strong anion exchange resin Dowex™ 1-× 8 in an off-line matrix separation and pre-concentration approach prior to determination by ICP-SFMS. The method allows simultaneous processing of four 100 mL samples at a flow rate of up to 2 mL min − 1 in an ultra-clean manifold. Enrichment factors of 40 could be achieved with elution into 2.5 g of a mixture of HNO 3 /HCl, yielding adequately low detection limits to obtain open ocean profiles. Quantification was performed by matrix-matched calibration and internal standardization. To validate the accuracy of this approach, isotope dilution analysis was also used. The applicability of the method was demonstrated on a suite of reference samples and depth profiles collected during the 2009 2nd U.S. GEOTRACES Intercalibration cruise in the eastern North Pacific. [ABSTRACT FROM AUTHOR]

Abstract: Distributions of iron and nitrate in the central California Current System upwelling regime (cCCS) from 34 to 41°N were determined during cruises in May 2010 and August 2011. High spatial and temporal resolution data for dissolved Fe and (nitrate+nitrite) in the cCCS from this study greatly expands upon previous studies that were narrower in scope (e.g., focused on just the Monterey Bay region). Shelf sediments from mid-shelf mud belts in this region provide the dominant source of Fe, and there are areas in the cCCS where insufficient Fe is upwelled to accompany elevated levels of other macronutrients (nitrate, phosphate, silicate) to fuel extensive diatom blooms. Surface dissolved Fe concentrations were related to continental shelf width and upwelling strength, and surface Fe concentrations tended to be lower in the late summer than early spring. We present extensive benthic boundary layer (BBL) dissolved and leachable particulate Fe data from both seasons in the mid-shelf region along the central California coast. Leachable particulate Fe concentrations were strongly related to the width of the mid-shelf mud belts (i.e., the continental shelf between the 50 and 90m isobaths). Dissolved Fe concentrations in the BBL over the mid-shelf were generally highest in wide mud belt areas as well as in areas with very low dissolved oxygen concentrations but did not show a clear seasonal trend. Evidence for probable Fe limitation in upwelled waters was found by using surface dissolved Fe: ratios and the estimated specific growth rate of coastal diatoms based on either Fe or concentrations. Several coastal upwelling regions with only moderate to narrow continental shelves (Pt. Arena to Cape Mendocino and the Big Sur Coast) exhibited evidence for Fe limitation in both the spring and summer upwelling seasons. [Copyright &y& Elsevier]

In order to establish the status of metal contamination in surface waters in the coastal ocean off Los Angeles, California, we determined their dissolved and particulate pools and compared them with levels reported in the 1970s prior the implementation of the Clean Water Act. These measurements revealed a significant reduction in particulate toxic metal concentrations in the last 33 years with decreases of ∼100-fold for Pb and ∼400-fold for Cu and Cd. Despite these reductions, the source of particulate metals appears to be primarily anthropogenic as enrichment factors were orders of magnitude above what is considered background crustal levels. Overall, dissolved trace metal concentrations in the Los Angeles coastal waters were remarkably low with values in the same range as those measured in a pristine coastal environment off Mexico's Baja California peninsula. In order to estimate the impact of metal contamination on regional phytoplankton, the internalization rate of trace metals in a locally isolated phytoplankton model organism (Synechococcus sp. CC9311) was also determined showing a rapid internalization (in the order of a few hours) for many trace metals (e.g., Ag, Cd, Cu, Pb) suggesting that those metals could potentially be incorporated into the local food webs. [ABSTRACT FROM AUTHOR]

Abstract: Mesoscale anticyclonic eddies in the Gulf of Alaska are an important mechanism for cross-shelf exchange of high iron, low nitrate coastal waters and low iron, high nitrate offshore waters. A Kenai eddy was sampled in September 2007, 8 months after formation. The subsurface eddy core layer contained reactive iron concentrations more than eight times greater than waters at the same depths outside the eddy. The subsurface core of the Kenai eddy (25.4≤σ θ ≤25.8) is suggested to be seasonally important as these waters can be brought to the surface with storm events and deep winter mixing. The deeper core layer (25.8≤σ θ ≤27.0) is suggested to be a source of iron to HNLC waters on a longer timescale, due to isopycnal mixing and eventual eddy relaxation. The subsurface and deeper core layers are important reservoirs of iron that can promote and sustain primary productivity over the lifetime of the Kenai eddy. In addition, dissolved and leachable particulate manganese are shown to be excellent tracers of eddy surface and subsurface waters, respectively. [Copyright &y& Elsevier]

Near-surface waters ranging from the Pacific subarctic (58°N) to the Southern Ocean (66°S) contain the neurotoxin domoic acid (DA). associated with the diatom Pseudo-nitzschia. Of the 35 stations sampled, including ones from historic iron fertilization experiments (SOFeX, IronEx II), we found Pseudo-nitzschia at 34 stations and DA measurable at 14 of the 26 stations analyzed for DA. Toxin ranged from 0.3 fg-cell-1 to 2 pg-cell-1, comparable with levels found in similar-sized cells from coastal waters. In the western subarctic, descent of intact Pseudo-nitzschia likely delivered significant amounts of toxin (up to 4 μg of DA·m-2·d-1) to underlying mesopelagic waters (150-500 m). By reexamining phytoplankton samples from SOFeX and IronEx II, we found substantial amounts of DA associated with Pseudo-nitzschia. Indeed, at SOFeX in the Antarctic Pacific, DA reached 220 ng·L-1, levels at which animal mortalities have occurred on continental shelves. Iron ocean fertilization also occurs naturally and may have promoted blooms of these ubiquitous algae over previous glacial cycles during deposition of iron- rich aerosols. Thus, the neurotoxin DA occurs both in coastal and oceanic waters, and its concentration, associated with changes in Pseudo-nitzschia abundance, likely varies naturally with climate cycles, as well as with artificial iron fertilization. Given that iron fertilization in iron-depleted regions of the sea has been proposed to enhance phytoplankton growth and, thereby, both reduce atmospheric CO2 and moderate ocean acidification in surface waters. consideration of the potentially serious ecosystem impacts associated with DA is prudent. [ABSTRACT FROM AUTHOR]

Abstract: This study examines the distribution of leachable particulate iron (Fe) in the Columbia River, estuary, and near-field plume. Surface samples were collected during late spring and summer of 2004–2006 as part of four River Influence on Shelf Ecosystems (RISE) cruises. Tidal amplitude and river flow are the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides. Near the mouth of the estuary, leachable particulate Fe [defined as the particulate Fe solubilized with a 25% acetic acid (pH 2) leach containing a weak reducing agent to reduce Fe oxyhydroxides and a short heating step to access intracellular Fe] averaged 770 nM during either spring tide or high flow, compared to 320 nM during neap tide, low flow conditions. In the near-field Columbia River plume, elevated leachable particulate Fe concentrations occur during spring tides and/or higher river flow, with resuspended shelf sediment as an additional source to the plume during periods of coastal upwelling and spring tides. Near-field plume concentrations of leachable particulate Fe (at a salinity of 20) averaged 660 nM during either spring tide or high flow, compared to 300 nM during neap tide, low flow conditions. Regardless of tidal amplitude and river flow, leachable particulate Fe concentrations in both the river/estuary and near-field plume are consistently one to two orders of magnitude greater than dissolved Fe concentrations. The Columbia River is an important source of reactive Fe to the productive coastal waters off Oregon and Washington, and leachable particulate Fe is available for solubilization following biological drawdown of the dissolved phase. Elevated leachable Fe concentrations allow coastal waters influenced by the Columbia River plume to remain Fe-replete and support phytoplankton production during the spring and summer seasons. [Copyright &y& Elsevier]

Abstract: A lower trophic level NPZD ecosystem model with explicit iron limitation on nutrient uptake is coupled to a three-dimensional coastal ocean circulation model to investigate the regional ecosystem dynamics of the northwestern coastal Gulf of Alaska (CGOA). Iron limitation is included in the NPZD model by adding governing equations for two micro-nutrient compartments: dissolved iron and phytoplankton-associated iron. The model has separate budgets for nitrate (the limiting macro-nutrient in the standard NPZD model) and for iron, with iron limitation on nitrate uptake being imposed as a function of the local phytoplankton realized Fe:C ratio. While the ecosystem model represents a simple approximation of the complex lower trophic level ecosystem of the northwestern CGOA, simulated chlorophyll concentrations reproduce the main characteristics of the spring bloom, high shelf primary production, and “high-nutrient, low-chlorophyll” (HNLC) environment offshore. Over the 1998–2004 period, model-data correlations based on spatially averaged, monthly mean chlorophyll concentrations are on average 0.7, with values as high as 0.9 and as low as 0.5 for individual years. The model also provides insight on the importance of micro- and macro-nutrient limitation on the shelf and offshore, with the shelfbreak region acting as a transition zone where both nitrate and iron availability significantly impact phytoplankton growth. Overall, the relative simplicity of the ecosystem model provides a useful platform to perform long-term simulations to investigate the seasonal and interannual CGOA ecosystem variability, as well as to conduct sensitivity studies to evaluate the robustness of simulated fields to ecosystem model parameterization and forcing. The ability of the model to differentiate between nitrate-limited, and iron-limited growth conditions, and to identify their spatial and temporal occurrences, is also a first step towards understanding the role of environmental gradients in shaping the complex CGOA phytoplankton community structure. [Copyright &y& Elsevier]

Abstract: Following basin-wide contamination from industrial emissions and urban development, total dissolved copper concentrations in some regions of San Francisco Bay have exceeded national and state guidelines for water quality. In the face of dramatic improvements in wastewater treatment and point source control, persisting elevated dissolved copper concentrations in the Bay have prompted multiple studies and extensive monitoring of this estuary since 1989. Statistical analyses of monitoring data show that total dissolved copper concentrations have declined in the North (by 17%) and South (29%) San Francisco Bay as well as in the Southern Sloughs (44%) from 1993 to 2001. Concentrations remain elevated in the farthest reaches of the Bay (Delta and Estuary Interface), and in the Central Bay. Dissolved copper concentrations throughout the Bay have also been positively correlated (, , ) with dissolved organic matter, supporting results from complimentary chemical speciation studies which indicate that high-affinity copper-binding organic ligands dominate the chemical speciation of dissolved copper in the Bay. These organic ligands typically bind>99.9% of the dissolved copper, effectively buffering the system against small changes in dissolved copper concentrations, and maintaining free Cu2+ concentrations well below the toxicity threshold of ambient aquatic microorganisms. In response to these findings, site-specific water quality criteria for dissolved copper concentrations are now being developed by the Regional Water Quality Board to provide a more appropriate standard for copper toxicity in the Bay—one based on its chemical speciation and bioavailability. [Copyright &y& Elsevier]

Abstract: Surface transects and vertical profiles of macronutrients, dissolved iron (D-Fe), and dissolved manganese (D-Mn) were investigated during August 2003 in the southeastern Bering Sea. We observed iron-limited, HNLC surface waters in the deep basin of the Bering Sea (15–20μmol/kg nitrate, ∼0.07nmol/kg D-Fe, and ⩽1.0nmol/kg D-Mn); nitrate-limited, iron-replete surface waters over the shelf (<0.1μmol/kg nitrate, 0.5–4nmol/kg D-Fe, and 2–33nmol/kg D-Mn); and high biomass at the shelf break (“Green Belt”), where diatoms appeared to have been stressed by low D-Fe concentrations (<0.3nmol/kg). Sources of nitrate and iron to the Green Belt were investigated. A mixture of Aleutian North Slope Current water (with elevated, but non-sufficient iron concentrations relative to its high nitrate concentrations) and surface waters from the vicinity of the Bering Canyon (with lower nitrate concentrations, but similar dissolved iron concentrations) was carried along the shelf break by the Bering Slope Current. This water mixture provided macro- and micronutrients at the southern end of the shelf break. The oceanic domain supplied additional macronutrients to Green Belt waters, while the bottom layer of the outer shelf domain supplied additional macro- and micronutrients through enhanced vertical mixing at the shelf break. Surface waters near the Pribilof Islands, where the highest surface D-Fe concentrations were observed (∼5–6nmol/kg), represent a potential source of additional iron to Green Belt waters. During summer, the subsurface water of the middle shelf domain is a potential source of nitrate to the nitrate depleted waters of the shelf. In this subsurface cool pool, we observed evidence of substantial denitrification with lower than expected nitrate concentrations. [Copyright &y& Elsevier]

Phytoplankton community structure in the eastern Equatorial Pacific (EEP) and the Peru upwelling system was determined using ChemTax analysis of pigment data. Photosynthetic efficiencies (Fv : Fm), concentrations of macronutrients, iron (Fe), and the redox proteins flavodoxin (Flv) and ferredoxin (Fd) were used to assess the physiological status of the algal communities with respect to Fe. Diel periodicity in Fv :Fm ratios was observed in Fe-stressed populations of Prochlorococcus and type 4 haptophytes (Phaeocystis) in the EEP with daytime values (0.05-0.30) displaying a distinct noontime minimum. On the Peruvian continental shelf, upwelling of Fe-rich subsurface waters led to massive diatom blooms (reaching chlorophyll a [Chl a] values >45 µg L-1) with near-maximal photosynthetic efficiencies (Fv: Fm >0.6). Assimilation and luxurious uptake of Fe, scavenging processes, and Ekman transport off the shelf break led to rapid decreases in Fe concentration and dramatic shifts in phytoplankton assemblages. The shelf break region was dominated by cryptophyte populations with relatively high photosynthetic competency (Fv:Fm = 0.4-0.5). In this region, subnanomolar Fe concentrations limited further diatom growth. As Fe concentrations decreased offshore, haptophyte (coccolithophorids and Phaeocystis) populations contributed approximately 40-80% toward the total Chl a concentration. Haptophyte populations were Fe stressed, as determined by high Fly indices (Flv [Flv + Fd]-1) and low photosynthetic efficiencies (Fv:Fm ∼0.3). The Flv index was very high in regions where Fe concentrations were <0.2 nmol L-1, but it was 0 when Fe levels were >0.4 nmol L-1. In the Peru upwelling, Fe concentrations between 0.2 and 0.4 nmol L-1 represented a transitional region that marked the threshold switch in community Fd and Flv expression. [ABSTRACT FROM AUTHOR]

Abstract: The use of a commercially available chelating resin with NTA-type functional groups for concentration of trace metals from seawater is described. Trace metal recoveries from this NTA Superflow chelating resin are pH dependent. At a pH of ≤2 only iron(III) and copper are quantitatively recovered from the resin. Iron(II) cannot be quantitatively recovered from this resin below a pH of 5. However, oxidation of acidified seawater samples (pH 1.7) with H2O2 prior to loading onto the resin has been demonstrated to allow quantitative recovery of total dissolved iron. Deferrioxamine and Rhodoturlic Acid, two commercially available siderophores were used to investigate the effect of strong Fe(III)-binding organic ligands on the ability to retain iron at different pH values. Acidification of seawater samples to pH 1.7 dissociates the iron complexed to these organic ligands, thereby allowing total dissolved iron and copper to be determined. Acidified samples from Monterey Bay were analyzed by a flow injection method coupled to ICP-SFMS detection using the NTA Superflow resin in the pre-concentration step. Results from this study show that when seawater samples are stored acidified (pH 1.7) over time, a portion of iron(III) is reduced to iron(II), thus necessitating the use of H2O2 to reoxidize the Fe(II) to Fe(III) prior to analysis. Total dissolved concentrations of iron and copper can be directly obtained on seawater samples at pH 1.7 with this method, eliminating the need to buffer the sample to a higher pH prior to column loading. This resin has the potential to be used in shipboard or in situ flow injection methods. [Copyright &y& Elsevier]

Presents a study which demonstrated the photochemical reactivity of siderophores produced by marine heterotrophic bacteria and cyanobacteria based on characteristic ferric ion complexes. Role of siderophores on the oceanic biogeochemical cycling of iron and the regulation of marine primary productivity; Materials and methodology of the study; Discussion on the results of the study.

Trace element (TE) fluxes and their residence times (Fe, Mn, Cu, Pb, Cd, and V) within the surface ocean were determined along the GEOTRACES East Pacific Zonal Transect (GP16/EPZT) and found to reflect the diverse physical and geochemical conditions encountered across the track. The TE flux from atmospheric deposition, vertical mixing, and upwelling into the mixed layer and into the particle production zone (PPZ) along the GEOTRACES EPZT transect were evaluated with 7Be-based methods developed in earlier works. A horizontal input flux is driven from east to west by the South Equatorial Current (SEC), and estimated advection velocities were applied to horizontal gradients in the distributions of several TEs to approximate this term. There is a minimum in atmospheric deposition in the central gyre, with higher fluxes to the east due to large near-shore aerosol TE loadings, and higher to the west due to greater precipitation-driven deposition velocities (V b). The 7Be-derived vertical diffusion (K z) values range from 2.5 to 39 m2/d (0.29 × 10−4 to 4.5 × 10−4 m2/s) with higher values generally within the nearshore upwelling region and the lowest values within the stratified central gyre. Manganese displayed a well-defined gradient extending from the nearshore stations into the central gyre such that the advective term is a major component of the total input flux, particularly within the central gyre. Relative to other inputs the atmospheric input of soluble Mn is only of minor importance. Unlike Mn, there is no discernable horizontal gradient in the dissolved Fe data and therefore, there is no horizontal component of flux. Nearshore removal processes are more intense for dissolved Fe than for dissolved Mn and as a result, dissolved Mn remains elevated much farther offshore than does dissolved Fe. For the stratified mid-ocean gyre stations, the total input of Fe from all sources is relatively small compared to the inshore stations, and atmospheric deposition becomes the dominant mode of input. Aerosol Fe solubility determined by a 25% acetic acid leach with hydroxylamine hydrochloride was much greater than that derived from a leach using ultra-pure deionized water. This led to significant differences in the residence time of Fe calculated for the mid-ocean gyre using these different solubilities. Generally, each element displays relatively short (weeks–months) residence times within the nearshore region of robust upwelling, reflecting large input terms and rapid removal. Moving offshore, total input fluxes decrease and the residence times of the TEs increase markedly until the western edge of the transect. There, relaxation of ocean stratification permits greater upward turbulent flux and greater rainfall leads to greater atmospheric input of TEs. • Trace element fluxes to the surface ocean were determined along the GEOTRACES EPZT. • Trace element residence times in the surface ocean were determined along the transect. • Trace element properties reflected diverse physical and geochemical conditions. [ABSTRACT FROM AUTHOR]

Organic dissolved iron (dFe)-binding ligands were measured by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) at multiple analytical windows (side reaction coefficient of salicylaldoxime, and 100) in surface and benthic boundary layer (BBL) samples along the central California coast during spring and summer. The weakest ligands were detected in the BBL at the lowest analytical window with average log in the summer and 10.8 ± 0.2 in the spring. Between 3% and 18% of the dFe complexation in the BBL was accounted for by HS, which were measured separately in samples by ACSV and may indicate a source of dFe-binding ligands from San Francisco Bay. The strongest ligands were found in nearshore spring surface waters at the highest analytical window with average log, and the concentrations of these ligands declined rapidly offshore. The ligand pools in the surface and BBL waters were distinct from each other based on principal components analysis, with variances in the BBL ligand pool explained by sample location, and variance in surface waters explained by water mass. The use of multiple analytical window analysis elucidated several distinct iron-binding ligand pools, each with unique distributions in the central California Current system. [ABSTRACT FROM AUTHOR]